EP1313279A1 - Verfahren zur Korrektur von Phasenverschiebungen in einem Signal und entsprechender Empfänger - Google Patents

Verfahren zur Korrektur von Phasenverschiebungen in einem Signal und entsprechender Empfänger Download PDF

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Publication number
EP1313279A1
EP1313279A1 EP01440383A EP01440383A EP1313279A1 EP 1313279 A1 EP1313279 A1 EP 1313279A1 EP 01440383 A EP01440383 A EP 01440383A EP 01440383 A EP01440383 A EP 01440383A EP 1313279 A1 EP1313279 A1 EP 1313279A1
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EP
European Patent Office
Prior art keywords
symbol
phase
receiver
received
current
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01440383A
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English (en)
French (fr)
Inventor
Ahmed Lahrech
Valérie Cueff
Jacques Eudes
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Alcatel CIT SA
Alcatel Lucent SAS
Original Assignee
Alcatel CIT SA
Alcatel SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Alcatel CIT SA, Alcatel SA filed Critical Alcatel CIT SA
Priority to EP01440383A priority Critical patent/EP1313279A1/de
Publication of EP1313279A1 publication Critical patent/EP1313279A1/de
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
    • H04L27/22—Demodulator circuits; Receiver circuits
    • H04L27/227—Demodulator circuits; Receiver circuits using coherent demodulation
    • H04L27/2271—Demodulator circuits; Receiver circuits using coherent demodulation wherein the carrier recovery circuit uses only the demodulated signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/06—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
    • H04L25/067—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection providing soft decisions, i.e. decisions together with an estimate of reliability
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset
    • H04L2027/003—Correction of carrier offset at baseband only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0044—Control loops for carrier regulation
    • H04L2027/0053—Closed loops
    • H04L2027/0055—Closed loops single phase
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0044—Control loops for carrier regulation
    • H04L2027/0063—Elements of loops
    • H04L2027/0067—Phase error detectors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0083—Signalling arrangements
    • H04L2027/0089—In-band signals
    • H04L2027/0093—Intermittant signals
    • H04L2027/0095—Intermittant signals in a preamble or similar structure

Definitions

  • the present invention relates to a method for compensating phase impairments in a signal, more particularly when the signal is modulated with a modulation comprising at least a phase modulation component.
  • the demodulation of a such signal is performed by multiplying the received signal at the receiver with a cosine signal generated at a local oscillator having the same period ⁇ . This operation enables to recover the phase ⁇ ( t ) of the received signal. Having knowledge of the signal phase and of the used modulation, the receiver is able to demodulate the signal.
  • a simple hard decision module can be used to associate a modulation symbol part of the used modulation constellation to a current received symbol.
  • phase error is evaluated in a phase loop with elevation of the phase to the power M.
  • M corresponds to the modulation constellation size.
  • MPSK Mary Phase-Shift Keying
  • this method cannot be applied to 16QAM (Quadrature Amplitude Modulation) or 64QAM because they are combined phase and amplitude modulations.
  • Another method consists in evaluating the phase error in a loop with feedback decision as described in figure 1.
  • An input signal is multiplied with a phase error estimation at a multiplier 11.
  • This signal is connected to a signal output and simultaneously submitted to a hard decision module 12.
  • Hard decision module 12 determines, according to a well-known method, the modulation symbol belonging to the used modulation constellation which corresponds the best to the current symbol after phase correction
  • the complex conjugate number of the selected modulation symbol is calculated at hard decision module 12.
  • the loop for determining the phase error estimation consists in multiplying at a multiplier 13 the signal at the output of hard decision module 12 with the input signal.
  • the result of this multiplication represents the phase error and the corresponding phase shift is used for correcting the next received symbol at multiplier 11.
  • phase errors computed on several previously received symbols are averaged at integrator 14 for obtaining a phase correction with reduced variance.
  • a particular object of the present invention is to provide a method for evaluating a phase error in a signal modulated with a modulation comprising at least a phase modulation component minimizing the number of wrong decisions especially in very noisy environment.
  • Another object of the invention is to provide a receiver for performing this method.
  • a phase correction term is evaluated as a predefined function of a phase difference between a current symbol after phase correction and hard decision and this symbol as received at the receiver input. Moreover, this phase difference is weighted by an indicator of the reliability of a hard decision result on the received symbol. The phase difference weighted by its reliability constitutes the error correction term and a corresponding phase shift is applied to the next symbols.
  • the method according to the present invention presents the advantage to give less weight to low reliable symbols while increasing the weight of more reliable symbols.
  • the influence of very noisy symbols in the phase correction loop is reduced.
  • This method gives also a higher resistance to disconnecting in a circuit-oriented transmission mode or high cell loss rate in a packet-oriented transmission mode.
  • the method according to the present invention presents further the advantage not to require a high processing power.
  • a predefined number of symbols and their corresponding phase correcting terms are combined to compute a phase error less subject to sudden radio propagation modifications.
  • the present invention will be described in the framework of a radio communication network. However, the present invention can be used in any other type of communication networks transporting modulated voice or data as a cable network or an optical fiber network.
  • the application of the present invention to a radio communication network as described below should be viewed as not restrictive.
  • FIG. 2 represents a receiver according to the present invention.
  • the receiver comprises a signal input 2in, a signal output 2out, a module 21 for compensating phase impairments.
  • the signal output 2out is preferably connected to further not represented receiver modules as an equalizer and / or a decoder.
  • the present invention concerns only phase compensation module 21 and does not depend on further modules present at the receiver.
  • Module 21 for compensating phase impairments comprises a hard decision module 211, a weighting module 212, a multiplier 213, an integration module 214, and a multiplier 215.
  • Signal input 2in is connected to multiplier 215 which is connected to signal output 2out.
  • a feedback loop consisting in hard decision module 211 connected to weighting module 212, itself connected to multiplier 213 and a integration module 214 is finally connected to multiplier 215.
  • a digital signal r(k) enters receiver over signal input 2in, a phase shift is applied to digital signal r(k) at multiplier 215 ( ⁇ and error ( k ) is the estimated phase error at the instant kTs, where T s is symbol duration).
  • the output of multiplier 215 is simultaneously submitted to the feedback loop and leaves module 21 at signal output 2out.
  • the signal forwarded to the feedback loop will be processed so as to generate the appropriate phase shift to be applied to a next input signal r(k+i) at multiplier 215.
  • Hard decision module 211 selects a modulation symbol dk out of the used modulation constellation which corresponds the best to the current received symbol c(k). For this purpose, the received symbol c(k) is compared to the modulation symbols dk of the modulation constellation. The modulation symbol having the lowest distance to the received symbol c(k) is selected. The distance is preferably an Euclidean distance between the points representing the different modulation symbols dk on a Cartesian coordinate system and the point corresponding to the current received symbol c(k). Preferably, the complex conjugate number of dk, dk*, is calculated at hard decision module 211.
  • Weighting module 212 determines a reliability indicator of the symbol dk after hard decision.
  • the reliability indicator is determined according to a predefined function. It shall for example depend on the inverse of the Euclidean distance between the received symbol c(k) and the symbol after hard decision dk on the Cartesian co-ordinate system representing the modulation constellation. Preferably, the lowest reliability is obtained when a symbol before demodulation is at the same distance of two hard symbols of the modulation constellation.
  • the reliability is preferably a value between 0 and 1.
  • hard decision module 211 dk*
  • the result of hard decision module 211, dk* is multiplied by the reliability ⁇ k at weighting module 212 and multiplied by the input symbol r(k) at multiplier 213.
  • the corresponding input symbol r(k) is preferably delayed at a delay module 216 by the processing time necessary to obtain the output of weighting module 212.
  • This processing time consists in the time duration for performing multiplication at multiplier 215, hard decision at hard decision module 211 and weighting at weighting module 212.
  • the output of multiplier 213 is called weighted phase difference.
  • the weighted phase difference (also called in the present embodiment error correcting term) is directly multiplied to the next symbol at multiplier 215.
  • the error correcting term is obtained by integration, at integration module 214, of several phase error correction terms obtained for several previously received symbols (r(k-1), r(k-2), ..., r(k-N)).
  • the weighted phase difference is stored at shift register 2141 which contains the weighted phase differences of the N previous demodulated symbols.
  • Summing module 2142 calculates the average value of all N weighted phase differences stored in shift register 2141 and generates the phase correction term which is multiplied by the next input symbol received at multiplier 215.
  • input symbols r(k) belonging to a preamble are submitted to a different processing.
  • This processing is preferably used for initialising module 21 for compensating phase error impairments.
  • a preamble corresponds to a sequence of symbols known at the receiver with 100 % reliability at the receiver. Then, hard decision followed by weighting is not necessary in this case. On the contrary, the expected symbol of the preamble is directly multiplied at multiplier 213 with the corresponding input symbol rk. In this case, no delay should be applied at delay module 216.
  • a switch 217 should be present between weighting module 212 and multiplier 213 to choose if the input of multiplier 213 should be the output of weighting module 212 or a known symbol of the preamble stored in a predefined memory location.
  • the position of switch 217 should be preferably controlled by a preamble detection module which is made aware of the reception of a preamble.
  • FIG. 3 shows a possible implementation of the method according to the present invention. The steps performed in the feedback loop will be described.
  • Step 31 consists in performing hard decision on current received symbol c(k) obtained from a symbol r(k) as received at the input of the receiver after a phase correction at multiplier 215.
  • the applied phase correction depends on a phase error calculated on previous symbols.
  • the hard decision consists in selecting a modulation symbol dk corresponding the best to received symbol c(k).
  • Step 32 consists in evaluating a reliability indicator of modulation symbol dk after hard decision.
  • Step 33 consists in evaluating a phase correction term as a predefined function of modulation symbol dk, reliability indicator and received symbol r(k).
  • Step 34 consists in averaging phase correction terms obtained for N previously received symbols.
  • Step 35 consists in multiplying the average phase correction term evaluated at step 34 with a next symbol r(k+1) received at the module for compensating phase impairments 21.
  • Figure 4 is a diagram showing performances of the method according to the present invention compared to prior art methods.
  • the present invention has been tested in a bursted mode context of a LMDS system.
  • the diagram represents the number of wrong bytes per packet on the x-axis and the cumulated probability of this event on the y-axis.
  • a first curve 41 represents performances of system without retroactive phase loop where local oscillator are ideal (i.e. free from frequency drift). The wrong bytes are only due to gaussian noise. This curve is used as reference for evaluating the performance of system in presence of frequency drift.
  • a second curve 42 represents performances of a phase impairment compensation system with a conventional retroactive phase loop as described in figure 1 in presence of frequency drift.
  • a third curve 43 represents performances of a phase impairment compensation system with a retroactive phase loop according to the present invention in presence of frequency drift.
  • the randomly distributed frequency offsets have been chosen in an interval so that
  • Ts being the symbol duration.
  • This diagram shows an improvement of the system performance when using the method according to the present invention since curve 43 is closer to reference curve 41 than curve 42.
  • the invention can be used in bursted mode especially in the uplink transmission direction of a transmission network.
  • the successive packets received at a base station are transmitted by different terminals and then submitted to different phase errors due for example to different oscillator drifts at the different terminals. It is necessary, in this case, that the base station performs a new initialization of the module 21 for compensating phase impairment after each received packets.
  • the initialization is preferably realized during the reception of the packet preamble.
  • the invention may also be used with the same advantage in a continue (non-bursted) mode where successive packets are issued by the same transmitter. This would be the case in the downlink transmission direction where a base station broadcast a data or transmit a Time division Multiplex to different terminals. In this case, no re-initialization between packets is necessary.
EP01440383A 2001-11-14 2001-11-14 Verfahren zur Korrektur von Phasenverschiebungen in einem Signal und entsprechender Empfänger Withdrawn EP1313279A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP01440383A EP1313279A1 (de) 2001-11-14 2001-11-14 Verfahren zur Korrektur von Phasenverschiebungen in einem Signal und entsprechender Empfänger

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP01440383A EP1313279A1 (de) 2001-11-14 2001-11-14 Verfahren zur Korrektur von Phasenverschiebungen in einem Signal und entsprechender Empfänger

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EP1313279A1 true EP1313279A1 (de) 2003-05-21

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005086444A1 (en) * 2004-02-19 2005-09-15 Thomson Licensing Method and apparatus for carrier recovery in a communications system
EP2068521A1 (de) * 2007-12-07 2009-06-10 Advantech Advanced Microwave Technologies, Inc. QAM-Phasenfehlerdetektor
WO2009071433A1 (en) * 2007-12-07 2009-06-11 Advantech Advanced Microwave Technologies Inc. Qam phase error detector
US7940861B2 (en) 2007-12-07 2011-05-10 Advantech Advanced Microwave Technologies, Inc. QAM phase error detector
CN115580356A (zh) * 2022-12-05 2023-01-06 北京融为科技有限公司 一种相位噪声抑制方法和设备

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2721778A1 (fr) * 1994-06-23 1995-12-29 France Telecom Procédé d'estimation d'une erreur de phase résiduelle sur les échantillons d'un signal numérique démodulé, et procédé de correction correspondant.
US5799047A (en) * 1995-09-25 1998-08-25 Nec Corporation Carrier synchronization unit and synchronization method
US6249180B1 (en) * 1999-09-08 2001-06-19 Atmel Corporation Phase noise and additive noise estimation in a QAM demodulator

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2721778A1 (fr) * 1994-06-23 1995-12-29 France Telecom Procédé d'estimation d'une erreur de phase résiduelle sur les échantillons d'un signal numérique démodulé, et procédé de correction correspondant.
US5799047A (en) * 1995-09-25 1998-08-25 Nec Corporation Carrier synchronization unit and synchronization method
US6249180B1 (en) * 1999-09-08 2001-06-19 Atmel Corporation Phase noise and additive noise estimation in a QAM demodulator

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005086444A1 (en) * 2004-02-19 2005-09-15 Thomson Licensing Method and apparatus for carrier recovery in a communications system
CN1918873B (zh) * 2004-02-19 2010-11-03 汤姆森许可公司 通信系统中载波恢复的方法与装置
EP2068521A1 (de) * 2007-12-07 2009-06-10 Advantech Advanced Microwave Technologies, Inc. QAM-Phasenfehlerdetektor
WO2009071433A1 (en) * 2007-12-07 2009-06-11 Advantech Advanced Microwave Technologies Inc. Qam phase error detector
US7940861B2 (en) 2007-12-07 2011-05-10 Advantech Advanced Microwave Technologies, Inc. QAM phase error detector
CN115580356A (zh) * 2022-12-05 2023-01-06 北京融为科技有限公司 一种相位噪声抑制方法和设备
CN115580356B (zh) * 2022-12-05 2023-03-10 北京融为科技有限公司 一种相位噪声抑制方法和设备

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